Thermal treatment of particulate materials, such as drying and/or calcining, is a wide-spread practice in many industries. Thermal treatment generally involves the application of heat to materials to remove their moisture or volatile content. For example, in the alumina industry for the preparation of reduction-grade alumina (Al.sub.2 O.sub.3) or catalyst supports, alumina hydrate (Al.sub.2 O.sub.3.3H.sub.2 O) is subjected to a thermal treatment to remove at least a portion of the water content of the alumina hydrate. Also, in the cement industry, the final commercial product is obtained from the raw cement by subjecting the raw cement to a calcination treatment. Volatile materials are removed by thermal treatment from many other products before they can be utilized. This applies, for example, to coke manufacture where the starting product, such as green coke, has to be freed of its volatile content by calcination before it can be commercially utilized in the aluminum or steel industry. In the manufacture of refractory products, removal of moisture or volatile matter is a common processing step. In many cases, including, but not limited to, the above examples, the volatiles released in the heating process include the hydrogen moiety of the sample. This permits one to monitor the calcination, or drying process, with a proton nuclear magnetic resonance spectrometer.
All of these operations require energy input and due to the high cost of energy, it becomes not only desirable, but also imperative, to minimize the waste of energy. One way to optimize the thermal treatment process is to introduce only the required quantity of heat energy in the equipment, such as rotary furnaces, coke ovens, fluidized bed furnaces, shaft kilns and the like. By the term "required quantity of energy", that quantity of energy is understood which produces the desired heat-treated product.
In the past, product quality control tests aimed to determine the residual moisture and/or volatile content of the heat-treated material involved the classical treatment of subjecting the heat-treated material to a further thermal treatment in the laboratory. This type of analytical procedure is time consuming and by the time the results are obtained, substantial quantities of energy can be wasted. To reduce the time involved in the testing, control system were suggested which continuously monitor the temperature within the heat-treating equipment. This type of control, although rapid and reliable with regard to temperature measurement, does not provide a true picture as far as the quality of the heat-treated product is concerned. As a result, operators tend to employ higher temperatures, e.g., use more energy, to assure that the heat-treated product meets the required standards.
A more current method, which, instead of measuring the furnace atmosphere, determines the properties of the heat-treated material, employs a neutron gun moisture probe. The neutron gun moisture probe utilizes fast neutrons from an americium source and directs these neutrons to a dried or calcined target sample. Hydrogen in the target samples slows down some of the fast neutrons causing back-scattering of these slowed down neutrons to a Geiger counter where they will be counted. The count can be correlated with volume percent hydrogen in the target sample and hence the residual combined water content can be calculated. The calculated results can then be used to adjust the heat-input to the heat-treating equipment as needed. This process, although rapid, lacks the desired sensitivity. In addition, if accurate results are desired, the sample size has to be significant, generally in the neighborhood of several hundred pounds, which renders the method cumbersome for plant process control purposes.
It has now been found that nuclear magnetic resonance (nmr) can be utilized to rapidly and reliably determine the residual moisture and/or proton-containing volatile content of heat-treated particulate materials and the results of such determinations can be immediately applied to adjust plant operating conditions resulting in optimization of operations and significant energy savings.